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Homework Help: Variable Velocity Vehicle Project

  1. May 26, 2008 #1
    Hi everyone,

    We recently were assigned a Variable Velocity Vehicle Project (VVV) in my physics class. The idea is we are supposed to create a vehicle (with 4 wheels) that:

    1) That should travel 6.00m and keep moving an additional meter before stopping. In other words, it has to stop at 7 meters exactly.
    2) The vehicle must make the run with 9-13 seconds and make another one between 19-23 seconds, but the instructor assigns the time that we have to make it in, so for example, he can give us 10 and 22 seconds, and our car would have to travel 7m in 10 and 22 seconds.
    3) No batteries larger than 6V can be used and the total vehicle must fit within a cubic meter and any methods of propulsion except volatile fluids and animals(haha) may be used.
    4) The propulsion system could be external or internal, so ramps and moursetraps would be allowed

    I was thinking something around a falling mass that turns a gear and that has a string going around another gear which would turn the axel and in order to reduce or increase time, i could have 2 sets of gears, a larger one and smaller one and I could alter the height the mass falls from to adjust its length and time. Its a basic setup, but I cant really think of anything much more efficent or advanced. Any sort of tips or advice would be really appreciated.
  2. jcsd
  3. May 27, 2008 #2
    A few questions:

    i] How are you allowed to change some parameter of the vehicle that would result in the time taken for the travel.
    ii] Is the car supposed to stop on it's own?

    One thing you can do is, use a simple DC motor. The power supplied by the motor is given as: [itex]P = \frac{V^2}{R}[/itex]. You can use a small rheostat to change the 'R'. Thereby, by changing 'R', you can control the power supplied and hence the Angular Velocity of the motor. This is similar to what real-life cars do: change the power supplied by the engine.

    A falling mass system should work as well, but I doubt if it can sustain motion for as long as 9 - 13s.
    Last edited: May 27, 2008
  4. May 27, 2008 #3
    also.. i didn't exactly understand what you meant by: "That should travel 6.00m and keep moving an additional meter before stopping"
  5. May 27, 2008 #4
    To answer your questions:

    1) We are allowed the change any parameter of the car we like in order to adjust the time it takes, but it still must stop exactly at 7.00m
    2) The car can stop however we want it as long as we dont place anything on the course, so we cant just place a barrier at 7m to make the car stop. Most people just let the car slow due to friction.

    As for the traveling 6.00m, the car basically has to stop at 7.00m. The timed portion of the project only takes into account how long it takes for the car to travel 6.00m. The remaining 1m is just room we can use to stop the car. The most efficent car would be one that travels 6.00m quickly and then stops abruptly at 7m.
  6. Jun 1, 2008 #5
    One more thing that I just noticed:

    That car has to travel 6m in 9-13s and 13-23s. The exact times will be given by the instructor, so the resistor would have to be really percise in order to adjust it to the right amount. The thing im worried about is how to stop the car or cut the power to the motor after it has traveled the right amount of time. We arent allowed radio controllers or anything, so how would I be able to regulate the power output of the motor so that it only travels 6m?
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